The invention relates to an economically beneficial process for producing optical couplers which have a high mechanical stability and are very resistant to thermal and weathering effects.
In passive optical waveguide networks, couplers serve as optical components for distributing the light signals from incoming optical waveguides over outgoing optical waveguides. Such couplers are composed of a transparent body which is connected to optical waveguides at the light input and at the light output side. In addition to couplers which are produced by bonding or fusing transparent moldings to optical waveguides, couplers are also known which are produced by twisting bundles of optical waveguides and stretching the twisted place (cf. Agarwal, Fiber Integr. Optics 6 (1) 27-53, 1987).
The production of such composite couplers is, however, complex and expensive; in addition, the throughput attenuation of such known couplers is difficult to reproduce so that the power varies by more than 1 dB between the various output fibers.
Furthermore, couplers are known in which fiber bundles made of polymer optical waveguides are fused together by means of a shrink-on sleeve (DE-A-3,737,930, WO-89/02608). In a process in accordance with WO-89/02608, only incomplete contact is produced between the fused core fibers, the shrink-on sleeve and a so-called "filler rod", so that a disturbed core-cladding boundary layer is produced which results in large optical losses.
A further major problem of many couplers, for example of the "biconical taper" coupler or also the combination of the shrink-on sleeve technique and the "biconical taper" process, is an only inadequate mechanical stability, in particular in the vicinity of the mixing region, which can be reduced only by supporting measures. In order to meet the stability requirements demanded in automobile construction it is therefore necessary to fix the couplers produced in position in special housings.